The present invention relates to a new category of DVD-RAM optical disk media (herein called xe2x80x9cDVD-WORMxe2x80x9d (Write Once, Read Many), and particularly to one that enables the user to have the capability of allowing data to be written to a sector only once and read many times.
The 120 mm DVD optical disk products available in the market fit into three categories: DVD-RAM, which are writeable, erasable and re-writeable; DVD-R, which is a recordable write-once version; and DVD-ROM, which is a read only version.
DVD-RAM media is composed of a phase change material. The material is constructed such that the recording medium can take on one of two distinct states. One of the states is amorphous and the other state is crystalline. Each of these two states has reflectivity levels that are different. That is, the crystalline state has a high degree of reflectivity while the amorphous state has a lower degree of reflectivity. The difference in reflectivity is detected by the optics and associated circuitry within a DVD-RAM drive. It is this difference in reflectivity that enables data to be recorded and read back.
The process of writing data onto DVD-RAM discs is achieved by a phase change effect typically created in the following manner; the disk is rotated upon a spindle motor contained within the drive. As the disk rotates at a given speed, a laser assembly within the drive heats a minute region [spot] of the disc recording layer. Typically the surface area of the region of the media being heated by the laser is brought to a temperature above its melting point. As the material cools, the area of the media that was effected by the laser beam cools into an amorphous state. This minute region or spot, which is now in an amorphous state, now reflects light at a lower reflectivity level. This minute region of the media will stay in this state until a laser beam that contains sufficient energy returns the molecules to a crystalline state which in effect erases the data as was represented by the amorphous state.
As the laser beam intensity can be modulated at a very high frequency, the area of the disc that is heated is correspondingly very small and can be thought of as a mark or bit. The length of the mark, or the time the laser is turned on, can also be varied so that marks of different duration can be written.
DVD-R discs are considered xe2x80x98write-oncexe2x80x99 in that once the disc is written there is no concern that the data may be erased, overwritten, or altered. For a user to record information on DVD-R discs a unique drive which can write DVD-R media is required. Currently, DVD-RAM drives are unable to write to DVD-R discs. User data which is recorded on DVD-RAM media can be write protected, however, the method of write protection involves the setting (manually done by the user) of a mechanical tab on the cartridge case. When the cartridge is inserted into a DVD-RAM drive, the position of the write protect tab is typically sensed by a mechanical switch within the drive itself. This method of write protection creates areas of concern to the user who wishes to protect data.
The first area of concern is that a user may unintentionally forget to set the write protect tab to the write protect position and thereby allow overwrites of previously recorded data to occur.
The second area of concern is that user data may be intentionally overwritten or altered simply by changing the position of the write protect tab from xe2x80x98read onlyxe2x80x99 to xe2x80x98writexe2x80x99, overwriting or altering the data, and then resetting the position of the write protect tab from xe2x80x98writexe2x80x99 to xe2x80x98read onlyxe2x80x99.
The third area of concern is that the mechanical switch within the drive itself may fail or become intermittent and thereby not provide a reliable method of protecting data.
A fourth area of concern is the storage and use of DVD-RAM media within automated storage libraries. Depending on the design methodology utilized by the manufacturer of the automated storage library, the DVD-RAM media may or may not be stored in cartridges when resident in the library. For example, media may be removed from the cartridge and placed on a tray that is then stored within the library. One of the issues with removing the media from the cartridge is that once the media is removed from the cartridge the write protect capability of the write protect tab is lost. Therefore the user does not have the capability of protecting data when media is stored in this fashion.
Currently the need for a new category of DVD-RAM media is beginning to take shape in the marketplace. This category of media is one that enables the user to have the capability of allowing data to be written to a sector only once and read many times. For the purposes of this document this media shall be termed DVD-WORM (Write Once Read Many). The primary application for this new product type would be any application where data must be stored and protected in it""s original form without the possibility of intentional or unintentional altering or overwriting.
U.S. Pat. No. 5,233,576, issued to Curtis et. al., discloses an apparatus and method for defining magneto-optical disk media and an optical storage device that allows the media to be convertible from writeable to read-only.
The present invention differs significantly from Curtis in a number of ways.
First, there are differences in the underlying media technology. The present invention is to be used with DVD rewriteable media that is of the type known in the industry as xe2x80x9cphase change media.xe2x80x9d Phase change media uses a different write/read methodology than that of magneto-optical. Phase change media is originally in a crystalline state. Phase change data is written by heating a minute region of the media above its melting point. As it cools it takes on an amorphous state. The amount of light read back or returned to the optic assembly in the drive is based upon the degree of reflectivity of the media. Crystalline media will return more light than an amorphous bit. In contrast, magneto-optical drives write data by heating a minute region of the media to its Curie Temperature in the presence of a magnetic field. This sets the magnetic polarity to that of the applied external magnetic field. Magneto-optical drives read data based upon the angle of rotation of the light returned to the optic assembly in the drive.
Second, the international standards used are considerably different. Curtis is based on media structure defined by the ISO Standard 10089 for 130 mm magneto-optical media. In contrast, the present invention is based upon the logical structure as defined by the ECMA standard ECMA-272 2nd edition (1999) for 120 mm DVD Rewriteable Disk (DVD-RAM).
Third, Curtis allows, in the first embodiment, a sector to be written to as many times as desired until the xe2x80x98storage state bitxe2x80x99 has been changed to read-only state. In contrast, the present invention does not allow any rewriting of sectors under any condition. That is, any sector can be written only once. Once the sector is written, write protect flags arc set that protect the data in the written sector.
Fourth, the present invention utilizes two write protect flags to provide an added security level of write protection. In addition, the two write protect flags consist of multiple bytes in each flag. This is a more robust method than Curtis, which uses a single bit for data protection, as the probability of a single bit being misread is much greater than that of a multiple-byte repeating sequence being misread.
Fifth, the present invention is usable whether or not the media is mounted within a cartridge. Magneto-optical media, such as disclosed in Curtis, is typically mounted within a cartridge and is typically not removed from the cartridge. The magneto-optical cartridge can itself provide a write protect capability by the use of a slide switch. Unlike magneto-optical media, DVD-RAM media can be removed from Type II DVD-RAM cartridges or the DVD-RAM media can be purchased not in a cartridge. Once the media is removed from the cartridge, all write protect capabilities are lost. Use of DVD-RAM media not in a cartridge can be found in the industry in autochanger applications. Typically users of DVD-RAM media in this manner do not have write protect functionality available within the drive.
It is proposed that the 120 mm DVD-WORM 2.6 GB disc and the 120 mm DVD-WORM 5.2 GB disc would be identical, note the exceptions defined in this document, to the 2.6 GB and 5.2 GB capacity 120 mm DVD-RAM disc as defined by the following ECMA (European Computer Manufacturers"" Association) standards:
ECMA-273 (1998) Case for 120 mm DVD Rewriteable Disk (DVD-RAM)
ECMA-272 2nd edition (1999) 120 mm DVD Rewriteable Disk (DVD-RAM)
It is proposed that data should be written to and stored on 120 mm DVD-WORM optical disks in a manner consistent with the ECMA-272 standard for DVD-RAM with the following exceptions:
The DVD-WORM media itself would contain identification data that indicates that the media is of the type WRITE ONCE READ MANY (WORM) and is not of the type DVD-RAM.
The user data sectors themselves will contain sector write control information, flags, that will indicate if the user sector is blank (i.e. contains no user data) or if the user sector contains user data.
This identification data and specific sector write control information would differentiate this media type from the current DVD-RAM media types.
Using standard commands delivered to the drive via the standard interface, user data may be written to and read from the DVD-RAM drive that contains DVD-WORM media. The DVD-RAM drive firmware itself would require modification, by the drive manufacturer, to recognize the new DVD-WORM media type and also to perform the write once, read many, function.